In open heart surgery, it is necessary to by-pass blood from the heart to what is called an "extracorporeal support apparatus" which is also called a life-support system.
Because of its heavy work load and high oxygen requirements, the muscle mass of the heart can tolerate very little ischemia (reduction of blood supply to an area because of obstruction or constriction of the coronary arteries).
A common technique used to protect the ischemic myocardium during the surgery involves the use of induced hypothermic cardioplegia. The technique involves the infusion of a cardioplegic solution into the coronary arteries at a low temperature. The chemical composition of the solution is varied; each cardiovascular surgical team has its own "recipe." However, the one chemical in common to all cardioplegic solutions is potassium. When infused, the potassium causes an immediate arrest of the heart, and the low temperature immediately begins to reduce the heart's oxygen consumption rate. The immediate stoppage and rapid cooling of the myocardium seems to offer the maximum protection available at this time.
In heart surgery, life support machines are utilized to perform temporarily the function of the heart and lungs while the patient's heart is being surgically serviced such as the repair of heart wall lesions, installation of a valve, and bypass artery work. The life support machine must take the flowing blood from the patient, maintain the temperature, pressure, and flow rate within certain physiologic limits, and provide the lung function.
In the course of an operation of this type, it is essential that a change-over be accomplished from the natural heart function to the machine. This involves installation of a venous return catheter into the right atrium (chamber) of the heart to serve as a drainage supply connection to the pumping machine.
In addition to the use of the venous return catheter, it is also necessary to introduce blood from the life support system to the aorta of the heart through an arterial cannula to complete the circuit of the support system during the operation.
Once the change-over to the life support machine is accomplished, the heart must stop beating and be made motionless so that the delicate surgical corrections can be accomplished. To stop the heart, a clamp is placed across the aorta. This cuts off the supply of oxygenated blood to the coronary arteries that supply the heart muscle. The reduced oxygen supply would eventually stop the heart, however, it could also damage the myocardium.
To protect the myocardium, a cooled cardioplegia solution that contains potassium is introduced into the coronary arteries. The potassium causes the heart to arrest and the cooling reduces the oxygen demand and oxygen consumption rate of the heart.
This introduction of the cooled cardioplegic flow is accomplished by the introduction into the aorta of an aortic root cannula which is ultimately secured to the aorta by sutures and connected to the cardioplegia supply line.
The introduction of the aortic cannula is accomplished while blood is still in the heart and it is important that any escape of blood be carefully controlled. This is especially important in recent years due to prevalence of certain blood carrying diseases to which doctors and technicians should not be exposed.
The present invention is directed to the introduction of an aortic root cannula which is designed to allow safe connection of the cardioplegia supply to the aortic part of the heart without the uncontrolled escape of blood to the outside.
It is an object to provide a cannula which will control the vent of air from the cannula and to control the rate at which the pressurized blood fills the cannula. It is also an object to control the flow of blood when the needle introducer is removed in a manner in which the pressurized blood is sealed in the tube prior to disconnection of a luer. A further object lies in the needle design which retracts into a male luer to prevent accidental skin punctures and scratches with a contaminated needle.
In addition to use as an aortic root cannula, the basic device can be used as an arterial cannula using the same introducer system.
Other objects and features of the invention will be apparent in the following description and claims in which the principles of the invention are set forth together with details to enable persons skilled in the art to apply the principles and techniques of the invention, all in connection with the best mode presently contemplated for the invention.